Radioactive assay apparatus



M y 1952 E. G. SEGRE 2,597,535

RADIOACTIVE ASSAY APPARATUS Filed July 25, 1946 INVENTOR [MIL/0 6 $5 am:

y MZW ATTORNEY Patented May 20, 1952 RADIOACTIVE ASSAY APPARATUS EmilioG. Segre, Berkeley, Calif., assignor to the United States of America asrepresented by the United States Atomic Energy Commission ApplicationJuly 23, 1946, Serial No. 685,639

1 Claim. 1

This invention relates to a fission assay apparatus in which a singlesource of neutrons is utilized to irradiate a plurality of fissionablesamples.

The object of this invention is to provide fissionable sample assayapparatus employing a single source of neutrons adapted to be utilizedfor simultaneously irradiating a plurality of samples of fissionablematerial arranged in separate ionization chambers positioned around theneutron source.

Other and further objects of this invention will be apparent to thoseskilled in the art to which it relates from the following specification,claim and drawing.

Referring to the drawing briefly, the sole fi ure thereof illustrates anembodiment of this apparatus in a perspective view in fragmentary crosssection.

The lead house in comprises a frame structure on which is supported alead floor and a lead roof. Four pivoted doors H are respectivelymounted on the sides of this structure. On each of the doors is mounteda lead panel l2. The lead floor, the lead roof, and the lead doors forma completely enclosed lead house. On the interior wall of each of thedoors there is mounted an ionization chamber C and an associatedamplifier A. A high voltage of a thousand volts is supplied to each ofthe ionization chambers from a common high voltage supply l3. The outputof each of the amplifiers is connected respectively to a correspondingcounter. The high voltage supply and the counters are disposed at apoint of the laboratory remote from the lead house. Details of thecircuits of the high voltage supply, the amplifiers, and the countersare described in the copending application of Clyde C. Wiegand, SerialNo. 689,484, filed August 9, 1946 for Assay Apparatus, now abandoned.Within the lead house there is mounted a block of parafl'lne P or othersubstance adapted to absorb energy from fast neutrons. This block ofparaffine includes cavities X into which the ionization chambers areadapted to fit when the doors are closed.

At the top of the lead house there is mounted a lead compartment M. Thislead compartment is held in register with the center of the lead houseby means of a brass tube which extends through an opening in the centerof the roof of the lead house into a cylindrical cavity in the lowerportion of the compartment. This brass tube fits within a cylindricalopening at the top of the parafiine block. The lower end of the brasstube terminates at about the center of the paraffine block and restsupon a copper disk R disposed at the bottom of the vertical cavity inthe parafiine block. A source S of fast neutrons is arranged to be movedbetween an operative position at the bottom of this brass tube withinthe lead house and a safety position within the lead compartment. Thissource S comprises a brass capsule containing a radium-beryllium mixtureenclosed by a covered copper can Y. Attached to the lid of the coppercan is a rod [4 which extends through a vertical bore l5 passing throughthe upper end of the lead compartment. A cord l6 attached to the upperend of this rod passes over pulleys suitably supported in the roof ofthe assay room and terminates adjacent a hook on the wall of the assayroom adjacent the interiors. By manipulation of the cord the source Smay be lowered into its operative position within the lead house orraised to its safety position within compartment M. The source may beheld in the safety position by tying the cord IE to the hook. The sourceemits gamma rays which are absorbed by the walls, the floor, and theroof of the lead house when the source is in its operating position withthe doors closed and which are absorbed by the walls of the compartmentwhen the source is in its safety position.

In practice, the source S is always retained in its safety position aslong as any of the doors on the lead house is open and is moved to itsoperating position only when all of the doors are closed and an assay ofone or more samples disposed within the respective ionization chambers Cis to be performed. When the source is in its operated position, fastneutrons emitted therefrom are slowed up by the parafl'ine block P. Someof the resulting thermal neutrons are captured by the 235 component of auranium sample mounted within the ionization chamber C. As a result,fission products are formed which cause the gas within the ionizationchamber to be rendered conductive. Each of the resultant pulses producedactuates the corresponding counter. The number of such counts obtainedin a measured time interval is utilized in connection with othermeasurements to determine the relative abundance of the isotopescontained in the uranium sample.

While I have described the salient features of this invention in detailwith respect to one embodiment, it will of course be apparent thatnumerous modifications may be made within the spirit and scope of thisinvention and I do not desire therefore to limit the invention to theexact details shown except in so far as they may be defined in thefollowing claim.

What is claimed is:

In apparatus of the character described, the combination comprising ashielded house defined by an apertured top wall, a bottom wall spacedtherefrom and a plurality of intervening and interconnecting side wallsprovided with apertures and symmetrically disposed about a central axisnormal to said first walls, a plurality of shielded doors for saidsecond apertures mounted in said side walls equidistant from said axisand provided with fission chambers containing fissionable material, ahollow lead cylinder mounted on said apertured top wall above said houseand provided with a tubular member fitting snugly within said cylinderand extending into said house through said apertured top wall along saidaxis, an apertured lead closure for one end of said cylinder and held inregister therewith by studs substantially parallel with the longitudinalaxis of said cylinder, a capsule containing radium and berylliumslidably positioned within said tubular member and having aifixed to oneend thereof a rod extending through said apertured closure 4 wherebysaid capsule may be moved within said tube, and a neutron-deceleratorcomprising a body of paraffin disposed between said source and saidfission chambers and having a source cavity located substantially onsaid axis and a plurality of fission chamber cavities disposed radiallyabout said source cavity, there being substantially equal thicknesses ofparaflin between said source cavity and each of said chamber cavitiesand substantially greater thicknesses of paraffin between any two ofsaid chamber cavities.

EMILIO G. SEGRE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,206,634 Fermi et al July 2,1940 2,287,620 Kallman et a1 June 23, 1942 2,306,194 Swaisgood Dec. 22,1942 2,462,270 Lipson Feb. 22, 1949 2,477,648 Piggot et al. Aug. 2, 1949

